The “conductive pattern” referred to herein relates to a conductive pattern that contains both an organic component including a resin and an inorganic component including a conductive filler etc.
So-called “polymer-type conductive paste” with a large amount of a particulate silver flake or copper powder, or carbon particles mixed in a resin or an adhesive to form an organic-inorganic composite conductive pattern as described above has come into practical use. Generally, the method of forming a conductive pattern is classified into a method using screen printing (see, for example, Japanese Patent Laid-open Publication No. 1-253111 and Japanese Patent Laid-open Publication No. 2005-267859) and a method using a photocurable photosensitive conductive curable paste (see, for example, Japanese Patent Laid-open Publication No. 2003-162921), but use of a photocurable photosensitive conductive curable paste capable of accurately drawing a pattern of 50 μm or less and capable of being cured at a low temperature is becoming mainstream in response to the recent trend of line thinning and temperature lowering.
When the photocurable photosensitive conductive paste is used, a pattern of about several tens μm can be formed, adhesion with a film and a glass substrate tends to be deteriorated as the line width decreases. Mention is made of a method in which an epoxy resin is added for improving adhesion (see, for example, Japanese Patent No. 4034555 and Japanese Patent Laid-open Publication No. 2003-301018). However, depending on a type of epoxy resin, a paste coating film has poor storage stability so that the shape of the conductive pattern obtained is affected by a time period until exposure, or there is no effect on adhesion with a base material such as a resin film or glass.
When the amount of an epoxy resin is increased, initial adhesion is improved, but peeling easily occurs after a wet heat test. Further, when the amount of an epoxy resin is increased, resistance increases.
It could therefore be helpful to provide a photosensitive conductive paste that ensures good storage stability of a paste coating film, is capable of maintaining high adhesion under relatively low temperature curing conditions, and is capable of exhibiting high conductivity. It could also be helpful to provide a photosensitive conductive paste which has good adhesion after a wet heat test.